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GDL90 position sources

Instead of the iPhone or iPad's internal GPS, Navigator can take position from a GDL90 broadcast — the UDP protocol that most portable ADS-B receivers and many panel-mount boxes use to feed position and traffic to tablets over Wi-Fi.

Worth doing when:

  • You are flying with a Wi-Fi-only iPad, which has no GPS receiver at all.
  • Your panel GPS is more accurate or updates faster than the tablet's.
  • The tablet lives somewhere with a poor view of the sky — a kneeboard low in the cockpit, or under a metal-framed canopy.

Setting it up​

  1. On the ground, power up the receiver and join its Wi-Fi network from iOS Settings.
  2. Launch Navigator and tap Start Live Flight.
  3. Import your .fpl as usual.
  4. Under Location Source, choose GDL90.
  5. Fill in your planned legs and tap Start Live Flight.
  6. Grant Local Network access when iOS asks. Navigator cannot receive anything without it.
  7. Watch the header. A GDL90: NO DATA pill in orange means nothing has arrived yet; it turns green and reads GDL90 on the first ownship report.

Do all of this on the ground. The permission prompt, the Wi-Fi association, and the first-fix wait are all things you do not want on the takeoff roll.

The source is fixed for the flight

Location source is chosen before the flight starts and cannot be changed while flying. If GDL90 never connects, end the flight, go back, and start again on Device GPS.

What Navigator does on the network​

Two things, both on your local Wi-Fi:

  • Listens for GDL90 UDP datagrams on port 4000.

  • Announces itself every 5 seconds, broadcasting to port 63093 on 255.255.255.255:

    {"App": "Navigator", "GDL90": {"port": 4000}}

Some receivers stream continuously to anything on the network and the announcement is redundant. Others wait to be told a client exists and which port to send to. Navigator does both so either kind works without configuration.

What it reads from the stream​

Navigator decodes ownship reports (GDL90 message ID 10) and ignores everything else, including traffic. From each report it uses:

FieldUsed for
Latitude / longitudePosition, distance, and bearing
Horizontal velocityGround speed, takeoff detection, leg switching
TrackCourse
AltitudeDecoded but not used in scoring

Heartbeat messages are recognised. Traffic reports are ignored — Navigator is not a traffic display and will not show you other aircraft.

A field the receiver marks as unavailable is treated as missing rather than as zero, so a fix without a velocity reading will not be misread as a stopped airplane.

Compatibility​

Navigator implements the standard GDL90 framing and ownship layout, so it should work with any source that emits a conformant stream on the conventional port — Stratux, ForeFlight-compatible portable receivers, and panel boxes with a Wi-Fi GDL90 output.

It has been developed against a limited set of hardware. If your receiver broadcasts GDL90 but Navigator shows NO DATA, that is worth reporting — say what the device is and how it is configured. See Troubleshooting.

When to just use Device GPS​

GDL90 adds a Wi-Fi network, a permission, and a device that has to stay powered, all in the name of a better fix. For a cellular iPad or an iPhone with a decent view out the window, the internal GPS is entirely adequate for the accuracy Navigator needs — checkpoint radii are measured in tenths of a mile, not metres.

Use GDL90 because you have a Wi-Fi-only iPad or a genuinely poor mounting position, not because it sounds more precise.